This invention relates to an apparatus for the digital control of an analog signal and, in particular, to a circuit arrangement for varying an analog quantity such as voltage, an impedance or the like.
Adjustments of the audio volume, color saturation, contrast, brightness and the like in various receivers such as a television receiver are sometimes performed by the use of a remote control apparatus instead of manually operating each of the adjustment knobs provided as part of a receiver. In such a remote control adjustment, a transmitter and a receiver are usually employed for the remote control. The transmitter may be operated by a viewer and the receiver is incorporated in the cabinet of a television receiver proper. The transmitter of the remote control apparatus is manipulated by the television viewer to send instruction signals, which are aerially transmitted as ultrasonic waves or as electric waves or the transmission directly may be through wire means to the television receiver. Corresponding to the types of the instruction signals, the receiver of the remote control apparatus generates pulse-shaped control signals and applies these control signals to the circuits to be controlled such as a volume control circuit, a color saturation control circuit and the like. Since the above described circuits to be controlled are adapted to operate in such a manner that they vary their analog output such as a voltage, an impedance or the like in accordance with the number of pulses in the control signals, a digital control is conventionally used for controlling such circuits. The digital control devices of this type employed so far, are adapted to count and store the a number of pulses by means of an up-down counter, and to effect a switching among the electronic switches provided in a resistor circuit network in response to the counted output to thereby provide voltages from said resistor circuit network corresponding to said counted pulses. The digital control devices of the type described are, however, expensive and hence not suited for use in apparatus used in the home such as television receivers.